1. Field of the Invention
The present invention relates generally to phased array antenna systems, and more particularly to a conformal phased array antenna mounted on an extendible mast.
2. Description of the Prior Art
The modern submarine requires high data rate communications to keep apprised of the constantly changing environment in which it operates. While submerged, the submarine uses its sonar systems to monitor the undersea environment and uses Extremely Low Frequency (ELF) transmissions for communications. Due to the low frequency, ELF communications cannot be used for high data rate transmissions. In order to obtain surface information or to perform high data rate communications with a surface vessel or satellite, it is necessary for the submerged vessel to extend an antenna or other communication means above the water surface. U.S. Pat. No. 3,754,268 to Boyns provides a phased array antenna system mounted in the periscope of a submarine. When a Super High Frequency (SHF) communications link between the submarine and an earth-orbiting satellite must be established, the periscope is extended such that the antenna system is above the surface. The surface wake of current antenna systems, or the periscope wake of the Boyns antenna system, provides an easy visual target for hostile forces. Further, the protruding antenna structure or, in the case of the Boyns antenna system, the periscope itself, provides an easily attained radar target for hostile forces. For some means of communications and ship sensor systems, such as line of sight RF communications and electro-optic (EO) sensors, the submarine must surface, or at a minimum expose the sail to allow operation of the communications equipment and sensors within the sail of the submarine. Current submarine sails present a very large visual and radar target. To minimize this threat, future submarine sails will incorporate stealth technology, will be hydrodynamically shaped to minimize wake and will incorporate conformal phased array antenna technology, all well known in the art. For example, U.S. Pat. No. 5,512,906 to Speciale describes such a conformal phased array. There remains a need to provide a system for extending communications equipment and sensors above the surface while the sail and submarine remain submerged. The system must not degrade the stealth characteristics of the sail, must be an integral part of the conformal arrays proposed for the stealth sail and must itself minimize visual and radar targets when deployed.